With reference to FIG. 9, rotating electric machines 1 have a stator 2 and a rotor 3 housed in a casing 4. From each end of the rotor 3 a shaft 5 extends. The stator 2 and rotor 3 are usually provided with a cooling circuit for taking away the heat generated during operation.
The cooling circuit usually includes channels through the stator 2 and rotor 3 for a cooling fluid and coolers 8 to cool down the cooling fluid. The cooling fluid is the fluid contained in the casing 4 and can be air, hydrogen, argon or a different fluid. In addition, the electric machine also has one or more fans 9 to circulate the cooling fluid.
The fans 9 are connected to the shafts 5 such that, during operation, the shafts 5 activate the fans 9.
This configuration has some drawbacks.
In fact, the speed of the shafts 5 cannot be freely changed to adjust the operating condition of the fans 9 according to the cooling fluid actually needed. In other words, since the fans are designed to provide the cooling fluid needed at full load, during operation at part load they supply an amount of cooling fluid that is larger than the amount actually needed. This causes a waste of power for operating the fans 9 and can also cause cool zones inside of the electric machine.
In addition, the cooling fluid is first cooled in the coolers 8 and is then supplied to the fans 9; when the cooling fluid passes through the fans 9 to be supplied to the stator 2 and rotor 3 its temperature increases. Therefore the temperature of the cooling fluid is not optimised.